The objective of this research project is to identify functional changes induced in single midbrain, hypothalamic and limbic system neurons due to the facilitating effects of estrogen and progesterone on lordosis, a sexually-receptive postural response to lumbosacral stimulation in the golden hamster. The activity of single brain cells will be recorded in freely-behaving hamsters in order to identify specific hormone-dependent changes in neural functioning which result in the appearance of the lordosis response. The specific objectives include two studies. The first study will identify lordosis behavior related estrogen and progesterone effects on neurons of forebrain regions with a high binding capacity for these hormones. The nature and time course of lordosis-inducing estrogen and progesterone effects on the activity level, movement-related firing and responsiveness to lordosis trigger stimuli will be examined in the medial hypothalamus and limbic forebrain, particularly septal and amygdaloid regions. The second study will analyze the mechanisms underlying previously-observed ovarian hormone effects on the activity of dorsal midbrain (principally deep tectal) neurons with known, behavior-correlated firing patterns. Changes in excitability of these neurons will be monitored during the lordosis-inducing actions of estrogen and progesterone by examining: (1) synaptic driving by electrical stimulation of hormone-binding regions of the ventromedial hypothalamus and (2) synaptic and antidromic (i.e. backfired) responses to stimulation of subtectal midbrain regions which receive projections from the ventromedial hypothalamus. In the long-term perspective, the proposed research should provide a new, microphysiological view of the spatial and temporal dynamics of ovarian hormone effects on neural function and behavior. These results will compliment and extend the present understanding of the neurological actions of ovarian hormones, which is based more on techniques such as hormone implantation or assays and related biochemical approaches. With the growing recognition of significant gonadal hormone effects on human brain development and behavior, as well as the massive use of synthetic forms of ovarian hormones for contraceptive and therapeutic purposes, it becomes increasingly important to understand the neural actions of these compounds. The therapeutic potential of estrogens and progestins could be exploited to a greater degree, as it has been for other steroids, once a fuller understanding of the neural actions of these hormones is available.